Condensation freezing of soot particles from various sources

The role of soot particles for heterogeneous ice nucleation is uncertain due to significant differences in reported experimental results (Hoose & Möhler, 2012). The objective of this study was to investigate the soot particle properties relevant for heterogeneous condensation freezing. We have investigated condensation freezing of soot particles online with the continuous flow diffusion chamber SPIN (Garimella et al., 2016). Soot particles from various sources including cookstove biomass combustion, a heavy duty diesel engine and a soot generator (miniCAST, model 5201C, Jing ltd) were studied. Physico-chemical properties of the particles were studied online with a scanning mobility particle sizer (SMPS-3938, TSI), a soot particle aerosol mass spectrometer (SP-AMS, Aerodyne), an aethalometer (AE33, Magee Scientific), an aerosol particle mass analyzer (APM, Kanomax), a cloud condensation nuclei counter (CCNc, DMT) and in some cases a single particle soot-photometer (SP2, DMT). Soot particles with a wide range of physical and chemical properties were studied, and in most cases, freezing occurred close to homogeneous freezing conditions with a sample temperature close to -38°C. In a few cases, the soot particles facilitated heterogeneous condensation freezing at temperatures above -38°C. The cases with heterogeneous freezing occurring for temperatures above -38°C will be presented and discussed.

References:

Garimella, S. et al., Atmos. Meas. Tech., 9, 2781-2795, 2016, doi: 10.5194/amt-9-2781-2016.

Hoose, C., O. Möhler, Atmos. Chem. Phys., 12, 9817-9854, 2012, doi:10.5194/acp-12-9817-2012.

Acknowledgements

We thank the Swedish Research Council and Formas for financial support.